Lecture 31: Skeletal Muscle Part II

Question 1

What is length-tension relationship?

Answer 1

For an isometric contraction -> in which in which the length of the muscle does not change, maximum active force (tension developed) changes with the resting sarcomere length of the muscle

Question 2

Why does the length of sarcomere affect the maximum active force (tension developed)?

Answer 2

Degree of actin and myosin overlap changes with resting sarcomere length

Question 3

At what lengths can maximal force be produced?

Answer 3

2.0 - 2.2 micrometers

Question 4

What happens as the resting length of sarcomere becomes too long?

Answer 4

Maximum active force degrees at steady rate as degree of overlap between myosin and actin decreases

Question 5

What happens as the resting length of sarcomere becomes too short?

Answer 5

Filaments collide and interfere with each other reducing the amount of force that can be developed

Question 6

What is passive force?

Answer 6

The force produced due to elastic component of muscles -> as muscle is stretched connective elements resist this extension = passive force

Question 7

How do you work out total tension?

Answer 7

Sum of active tension (determined by length of sarcomere) and passive tension

Question 8

What is the relationship between active force and passive force?

Answer 8

Active force increases as muscles contract - length decreases -> this leads to the increase of passive force as connective elements resist extension to greater extent

Question 9

What is a motor-unit?

Answer 9

A motor-unit consists of a single motor neuron and all the muscle fibers it innervates

Question 10

What are the two parts to excitation-contraction coupling?

Answer 10

1: Neuromusclar junction
2: Calcium coupling

Question 11

Explain the calcium coupling stage of excitation-contraction coupling?

Answer 11

Action potential is conducted down t-tubules (in contact with sarcoplasmic reticulum opening)

Voltage-gated calcium channels in the sarcoplasmic reticulum open allowing calcium ions to diffuse into the cytosol of the muscle fibre

Question 12

How does muscle contraction end?

Answer 12

Muscle contraction ends when calcium ions are actively pumped back into the sarcoplasmic reticulum by calcium ion pumps

Question 13

What are the sources of ATP for muscle metabolism?

Answer 13

1. Creatine phosphate
2. Anaerobic glycolysis
3. Aerobic metabolism

Question 14

Describe how energy is obtained from creatine phosphate

Answer 14

Creatine phosphate + ADP = creatine + ATP

Creatine phosphate is therefore an anaerobic source of energy (no oxygen required) and quickly spent <15s

Used for short bursts of energy

Question 15

Describe how energy is obtained from anaerobic glycolysis

Answer 15

Energy obtained without the use of oxygen from glucoe

Fast but inefficent as only 2 ATP per glucose

Used for 10-30s of maximal effort

Build up of protons limits anaerobic glycolysis as enzymes cannot function under highly acidic conditions

Question 16

Describe how energy is obtained via aerobic respiration?

Answer 16

32 ATP per glucose -> efficient

Requires oxygen -> good blood supply

Required for postural muscles and endurance exercises

Question 17

What are the two types of muscle fibres?

Answer 17

Type 1 (slow oxidative)
Type 2 (fast glycolytic)

Question 18

What are type 1 motor units?

Answer 18

Units with neurons innervating the slow efficient aerobic cells (maintain posture and walking)

Question 19

What are type 2 motor units?

Answer 19

Units with neurons innervating the large fibres that fatigue rapidly but develop large forces (jumping, weight lifting)

Question 20

How is force produced by muscles regulated?

Answer 20

1) Rate of stimulation of individual motor units

2) Total number of motor units recruited

Question 21

How does increased rate of stimulation increase force produced?

Answer 21

Temporal summation -> as increased frequency of stimulation occurs muscles do not relax between stimuli

Question 22

How does total number of motor units regulate force of muscles?

Answer 22

As more units are recruited tension increases

Fatigue resistance motor units are recruited first